Hydraulic tensioners have been widely used with timing belts and timing chains that transmit rotation between the crankshaft and one or more camshafts in an internal combustion engine. The purpose of these tensioners is to suppress vibration generated during the travel of the timing belt or chain, and to maintain proper tension.
In a hydraulic tensioner, oil is typically introduced, through a one-way check valve, into a high pressure chamber formed by a housing and a plunger. In one proposed tensioner, described in Japanese Laid-Open Publication No. 2002-206603 (On page (2), column 1, lines 2to 6; on page (4), column 5, lines 4to 28; on page (6), column 9, lines 19to 34; and in FIG. 1) a metal cylinder is fitted to a cylindrical hole formed in a housing. A hollow plunger, which fits slidably into the cylinder, is urged in the protruding direction by a compression spring, which is in engagement with a bottom plate formed on the cylinder. An oil chamber is formed by cooperation of the inside of the plunger and the cylinder. The bottom plate has a central hole for the inward flow of oil. A reduced diameter cylindrical hole is provided at the bottom of the cylindrical hole of the housing, and a check valve mechanism is fitted into the reduced diameter cylindrical hole. The check valve mechanism is pre-assembled, and comprises a cylindrical block having an oil passage, a ball seat fitted into the cylindrical block, a check ball, a coil spring urging the check ball against the seat, and a lid holding the coil spring in place. Abutment of the upper part of the cylindrical block with the bottom plate formed on the metal cylinder holds the check valve mechanism in place in the housing.
The hydraulic tensioner disclosed in the above-mentioned Japanese Laid-Open Publication No. 2002-206603 has several problems. First, because, the ball seat is press-fit into the cylindrical block when the check valve mechanism is pre-assembled, the inner circumferential surface of the block and the outer circumferential surface of the ball seat must be machined to a high working accuracy. The requirement for accurate machining leads to a high manufacturing cost. Second, when the check valve assembly is incorporated into the housing, the force exerted by the compression spring on the bottom of the metal cylinder is depended upon to hold the check valve assembly in the reduced diameter cylindrical hole. The dependency on the force exerted by the compression spring to hold the check valve assembly in place gives rise to difficulties in the assembly of the tensioner.
Accordingly, among the objects of the invention are the solution to the above-mentioned problems, reduction in the manufacturing cost of a hydraulic tensioner having a check valve assembly, and simplification of the assembly of the tensioner.